Need advice for rejected icon set

Hi guys! I just had a rejection for some icons I submitted a week ago.
I’m not sure why it got rejected :sweat_smile:

Here’s a screenshot of the preview :

And here’s the response from the reviewer :
“Unfortunately your submission doesn’t meet our current minimum technical quality requirements for the category it was submitted to. Please consider taking some time to familiarize yourself with our current library and quality levels of popular items before resubmitting.”

Any advice will be much much appreciated!